This disclosure relates to thermoplastic compositions, methods of manufacture, and articles and uses thereof.
Polycarbonates and its copolymers, with their balance of properties including transparency, low color, impact resistance, ductility, and melt flow, are useful in applications where both excellent toughness and UV stability is needed. For applications where more stringent toughness properties are desired, including low temperature impact and ductility, thick section impact and ductility, and retention of ductility on heat aging, an unalloyed polycarbonate itself may be insufficient.
Toughness and ductility in polycarbonates may typically be further improved by adding core/shell impact modifiers. However, use of impact modifiers can affect the UV stability of a polycarbonate so modified, which can affect the resistance of a material to color change (i.e., color stability); loss of gloss (i.e., gloss retention), particularly in opaque compositions; loss of transmission/increase in haze for transparent resins; or loss of other physical properties upon exposure to UV light such as from sunlight or artificial light. Impact modifiers based on unsaturated elastomers, such as butadiene, can react photolytically, and therefore have low UV stability, whereas acrylate based impact modifiers generally have a lower photolytic reactivity and greater UV stability. Nonetheless, acrylate core/shell impact modified polycarbonates may suffer from other drawbacks including increased gloss loss on weathering; visual defects affecting part aesthetics including gate blush (a dull or discolored area at the gate injection site of an injection molded article) and flow lines (a mark on a molded plastic article formed at the meeting of two flow fronts) formed during molding; and increased opacity. Impact modifiers are typically intrinsically non-miscible components that can form separate domains that scatter light and provide a white appearance. Thus, in addition to reduced transmission due to the increase opacity, the whiteness of the blend color may increase, which can adversely affect the preparation of colored impact modified polycarbonate compositions where it is desirable to have both the improved impact properties as well as high gloss, and depth and richness of color.
There accordingly remains a need in the art for polycarbonates having good melt stability, improved ductility, and low haze for use in thermoplastic compositions. In addition, the resins should not produce objectionable odors during melt processing. The thermoplastic compositions prepared therefrom also desirably have improved color capability, weatherability, and gloss retention.